For papermaking with straw as specified in the prior art, the raw materials used are mainly the straws of plants from annual grass family and mallow family. The applied papermaking process generally consists of straw cutting, screening, dedusting, digestion, washing, screening and cleansing, bleaching, washing, beating and papermaking.
In the prior art, the ammonium sulfite method is used for preparing non-woody fiber raw material pulp. It is characterized by mild digestion, so as to avoid the damage of the strong alkali on fibers, enhance the strength of the pulp, increase the yield, reduce the broken end damages of the papers, and achieve high rate of finished products.
After the straw raw material in question is digested in ammonium sulfite, the cellulose is extracted as the raw material for papermaking. The remaining black liquor can be used as fertilizer. However, since the water content in the digested black liquor of ammonium sulfite is high, the storage and transportation are not convenient.
CN200510086269 discloses a method for preparing commercial organic fertilizer out of waste liquor from pulping and papermaking by the ammonium sulfite method; Comprehensive Treatment Technology for Papermaking Wastewater by Ammonium Sulfite Method (Environment And Sustainable Development, Page 36 to Page 37, Volume 1, 2006) reports a kind of waste treatment method that separated the papermaking wastewater into digested black liquor, mid-phase water and white water, all of which will be separately treated and utilized, so as to achieve the comprehensive standards. However, during the black liquor evaporation of the method in question, the energy consumption is high, so is the cost. In addition, the ammonium sulfite decomposes during evaporation, so there is a certain content of ammonia in the condensate, which belongs to the ammonia nitrogen pollutant. Therefore, the condensate can not be directly discharged. It is required to additionally treat the condensate, which further increases the cost. Moreover, the non-woody fiber raw material pulp prepared with ammonium sulfite method is hard to bleach. During the bleaching, the dosage of bleacher is increased, which further increases the cost and enlarge the pollution source.
Besides the disadvantages mentioned above, the papermaking with non-woody fiber also has the following disadvantages:    1 The paper pulp fiber is small, low in strength and poor in filtration performance, and the quality of the paper made from the paper pulp fiber has a relatively low quality;    2 The water consumption is as high as 100 m3 to 150 m3 per ton of pulp;    3 There are many small fibers in the black liquor, the content of polysaccharides is high, the interference is taken by Silicon, and the structure of lignin is complex, all of which result in the low concentration of black liquor and difficulties in treatment of black liquor;    4 The discharge of COD and BOD severely exceeds the standards. The discharge of wheat straw pulp COD in China accounts for more than 74% of the total discharge in the entire papermaking industry;    5 In the waste liquid of chlorine bleaching, there are not only the common pollutant factors for water environment such as COD and BOD, but also highly toxic products such as trichloromethane, dichlorophenol, trichlorophenol, and dioxin, chlorofuran, etc.
In conclusion, during the papermaking with straw raw material, the improvement of only individual step can never realize the comprehensive purpose of water conservation, energy conservation, consumption reduction, efficiency increase, and high quality. Only the breakthroughs in the technologies of pulping, papermaking, energy conservation and consumption reduction can achieve the efficient and circular utilization of resources, and realize the goal of sustainable development of papermaking industry.
Therefore, the present invention is filed.